The invention relates generally to a continuous casting mold which is adjustable during casting so as to change the dimensions of a continuously cast strand.
More particularly, the invention relates to an arrangement for remotely adjusting a movable wall of a continuous casting mold during casting in order to change the dimensions of a strand being cast.
The West German Auslegeschrift No. 2 340 768 discloses a generally vertical continuous casting mold having a pair of oppositely disposed wide walls, as well as a pair of oppositely disposed narrow walls which are received between the wide walls. The walls cooperate to define a rectangular cavity for casting. The narrow walls are pivotable, and also translatable, for the purpose of effecting a change in the width of the mold cavity, and hence the width of a strand being cast in the mold. This strand has a rectangular cross section.
An arrangement is provided which makes it possible to remotely adjust the narrow walls during a cast, i.e. without interrupting the casting operation. The arrangement includes a pair of spindles for each narrow wall, and one of these spindles is articulated to an upper portion of the respective narrow wall while the other spindle is articulated to a lower portion of the wall. Each of the spindles associated with a narrow wall has a worm drive, and the two worm drives are driven by a common motor via a drive shaft, as well as appropriate gears and couplings. The connection between the motor and the respective spindles is such that the corresponding narrow wall may pivot or translate under the action of the motor.
The connection between a motor and the worm drive of the corresponding lower spindle includes a connecting shaft and an associated clutch. The clutch makes it possible to operate the worm drive for the upper spindle without that for the lower spindle to thereby pivot the respective narrow wall. The operation of the motor and the clutch are regulated in such a manner that the narrow wall can be automatically adjusted during a cast in dependence upon the casting speed, etc.
A drawback of the above arrangement is that air gaps are created between a respective narrow wall and the solidified outer shell of the continuously cast strand when the narrow wall is pivoted. Since this increases the risk of a breakout, i.e. a rupture of the outer shell with an accompanying escape of the molten core confined thereby, the narrow wall must be adjusted at very low speeds in order to minimize air gap formation. This results in an undesirably long transition section which is a conical section of the strand that, during a width change, develops between the rectangular portion of the strand having the original dimensions and the rectangular portion of the strand with the new dimensions. Inasmuch as the transition section is not suitable for further processing, it is preferred to minimize its length.
The known arrangement has another drawback in that it is not possible to pivot a narrow wall on an axis located in the region of the upper portion of the wall.
A further arrangement for adjusting the narrow walls of a mold is disclosed in the European Pat. No. B1-00 28 766. This arrangement has two independent adjusting units for each narrow wall. Each of the adjusting units for a respective narrow wall has its own drive, and the two drives are regulated independently of one another by a computer. In this manner, any desired movement of a narrow wall may be achieved.
The latter arrangement has the drawback that the relative rotational speed of the two drives associated with a narrow wall is controlled purely electronically. Should there be an electronic malfunction, e.g. in the computer, the narrow wall may assume an unacceptable inclination while moving at maximum speed. This, in turn, increases the chance of a breakout.